The present invention relates to a method of driving a cathode ray tube having a flat configuration, for use in such applications as color TV receivers, computer display terminals, etc.
Such a flat type of cathode ray tube contains a plurality of electron beam sources for producing respective electron beams, a group of control electrodes for modulating the levels of beam current of the respective electron beams in accordance with display data, and a group of focusing and deflection electrodes for producing horizontal and vertical deflection of the electron beams before the beams fall upon light-emitting material of the cathode ray tube screen. Generation and deflection of the respective electron beams are coordinated such as to combine the effects of the electron beams to produce a display picture on the cathode ray tube screen. With such a cathode ray tube, assuming a condition in which identical potentials are applied to all of the control electrodes, the levels of electron beam emission should ideally be identical for all of the emission sources. That is to say, if the data to be displayed represents a completely uniform level of display screen brightness (e.g. a completely white screen), then such a uniform display condition should be produced. However in practice, with prior art drive methods for such cathode ray tubes, this condition is not attained. Due to such factors as differences in the coating material formed on the cathodes to produce electron emission, slight deviations in size between different apertures in the control electrode through which the electron beams are passed, etc, it is found that there are significant differences between the emission characteristics of the electron beam sources. These differences result in conspicuous variations in screen brightness over the display screen, under a condition in which uniform display brightness should be produced.
In the following, the relationship between voltage applied between an electron beam source and a corresponding control electrode and the resultant level of electron beam current will be referred to as the beam emission characteristic, i.e. the problem of the prior art described above is a result of non-uniformity of beam emission characteristics between different electron beam sources of the cathode ray tube.